1. Field of the Invention
The present invention relates to a polarizing plate and a method for manufacturing the same. Further, the present invention relates to a protective film for polarizing plate. The polarizing plate of the invention can be used independently or as an optical film laminating the plate and form a visual display, such as a liquid crystal display, an organic electroluminescent (EL) display or plasma display panel (PDP).
2. Description of the Related Art
In a liquid crystal display, it is indispensable that polarizers should be arranged at both sides of a glass substrate that forms a top surface of a liquid crystal panel according to a picture formation method. Generally, polarizing plate laminating a polarizer, comprising a polyvinyl alcohol derived film and a dichroism substance such as iodine, and a transparent protective film such as triacetyl cellulose film is used.
The above described polarizing plate is manufactured by laminating a polarizer and a transparent protective film by adhesives. As the above-mentioned adhesives, for example, aqueous solution including polyvinyl alcohol and a cross-linking agent, and isocyanate derived adhesives, etc. are used. However, adhesion between a triacetyl-cellulose film used as the above-mentioned transparent protective film and the above-mentioned adhesives is not enough. Therefore, a triacetyl-cellulose film whose surface is saponified to improve adhesive property by being dipped in alkaline solution is used.
However, since a high-concentration alkali solution is used in saponification processing, it is accompanied by danger, and also has a large load to equipment, and thereby troubles, such as failure, may be easily induced. Moreover, when saponification processing is performed for a long time, concentration of an alkali solution used may be decreased and the adhesive improving effect by the saponification processing may often become inadequate. Furthermore, in disposal of a spent-caustic solution, there were problems, such as causing of a large quantity of wastewater.